Archive: When is Now?

First posted 28 June 2006. My view of time and consciousness is surprisingly close in this 11-year old post to what it is today, even though I had not been exposed at that time to the main elements that now underpin my reasoning.

Several pairs of unreconciled truths (as in best operating guesses) interest me deeply: Quantum mechanics & General relativity, Determinism & Free Will, Materialism & Consciousness.  These pairs are not unrelated, could indeed be different manifestations of the same chasm.  The paradox that may interest me most of all captures aspects of all three and is almost certainly inextricably entwined with each, and that is: Space-time & Temporal becoming.

The paradox has two elements.  The first, in a nutshell, is that our best understanding of space-time tells us that it is a complete, unchanging, four-dimensional (perhaps with seven further dimensions wrapped tightly around themselves, unextended) whole, but our direct experience is of a temporal flow with each moment different from the last.  All is constant, yet the only constant is change itself.

The second is that while space-time itself has no privileged set of parallel planes that can be called Nows (each inertial frame parses out space and time in a different way, with the Nows as planes at different angles to one another) , we each indisputably experience a clear distinction among past, present and future.  The flow from the latter to the former hearkens back to the first element of the paradox.

In an interesting paper, entitled "The Physics of 'Now'", James Hartle takes us some of the way towards a reconciliation.

Space-time
Space-time is a four-dimensional grid, with each point being an event.  If we label one axis as the the speed of light multiplied by time and the others as the space dimensions, then one can imagine two cones, extending in opposite directions parallel to the 'time' axis and meeting at a designated point, or event.  The one pointing back toward the Big Bang is the past light cone for that event, and the one opposite it is the event's future light cone.

There is a reason these are called light cones: given the chosen units of the time axis and the fact that nothing can travel at speeds exceeding the speed of light, all points (events) within the 'backward' light cone can be said to be in the given event's past, they could have played some part in the evolution that led to the given event's occurring.  Similarly, all points in the future light cone can possibly be affected by this given event.  Points outside these cones cannot be said to be in the given event's past or future.  They are what is called 'space-like' separated from it.

If we imagine that event or point as being one of many that make up the history, or world line, for a person as that person travels through life (and space and time!), then, within that person's frame of reference, the plane that runs through that event and is perpendicular to the time axis might be defined as a Now or instant for that person.  

But the thing is that that person's frame of reference is not privileged, is nothing special.  So although it might be called a Now for him, it is not a Now for the universe. Other people could be travelling at very great speeds relative to him, and their Nows would be askew with respect to his.

As it happens, all we humans exist very close to one another (on a cosmological scale), and we move only at very low velocities relative to one another (as compared to the speed of light).  So our Nows are for all intents and purposes not only parallel but even simultaneous.  Still, this is just a local accident.

IGUSes
Why do we distill the time dimension from the space ones and experience it as a flow from future to past?  Hartle believes it is a function of the way that we collect and process information.  Placing humans within a broader set of entities he calls Information Gathering and Utilising Systems (IGUSes), he models a simple IGUS to demonstrate his thinking.

In essence, we have 'registers' for current input and for memories of past input.  These registers contribute directly to conscious thought both directly and indirectly, the latter through subconscious updating of our 'schema' or underlying operational models for dealing with the world around us.  

In any moment, or more to the point, at any event along our world-lines, the 'current input' register is populated by what we are experiencing, the remaining registers are populated by what we experienced in each of several immediately preceding moments.  The direct 'feed' from the 'current input' register to conscious thought gives the sense of Now.  The fact that any brain state enfolds information from previous brain states ( in the other registers), gives a sense of both a past and of a  flow to time.  The future is not represented in any register but is rather the object of calculation in both conscious and subconscious processing.

But why does this flow move in one direction rather than the other, or rather than in both?  Hartle appeals to two old dears of physics, the 2nd law of thermodynamics (which states that entropy must always increase), and the nature of electromagnetic radiation.  I've talked about the first elsewhere.  The second is worth mentioning a bit more about.  Anything we see has radiated from some source.  Electromagnetic radiation only ever travels in that one 'direction' - from source outwards.  

In a sense, then, the past can simply be defined as the direction in time from when radiation strikes our retina to when it is (was) emitted.  Information only travels that way.  Since gathering and processing information is what we do, we naturally take on or assign this direction a prominent place, simply through our interactions with the world.

Questions unanswered
As ever, I'm sure that I've been less than perfectly true to Hartle's original argument, so do read his paper.

I will say, though, that I think he leaves two questions unanswered.  They may well fall outside the scope of his work, but they are related and interesting.  First, Hartle mentions repeatedly that we EVOLVED into the IGUSes we are, to process information as we do, because that is what worked.  He is doing nothing more than making one specific reference to the accepted truth of Darwin's thesis.  But when one thinks of space-time as a four-dimensional, unchanging and complete totality (as I believe it is), one can't help but think differently about evolution.

We no longer say, things are this way because they evolved to be so, and they evolved to be so because being so conveyed survival and reproductive benefits.  That is all true WITHIN the time dimension, but within the eternal space-time picture, that we are this way is just that we are this way.  Both our present state of evolution and every other step in its past and future exist eternally.  So one then asks, why is THAT so?  Why is it that this relationship within four-dimensional space-time exists?  I don't have an answer.  It is just SO.

Second, it is simple enough to refer to a given event on my world-line, look into the 'current input' register and say, "That is my Now".  But the interesting point is that EVERY ONE of the points on the 'conscious' segment of my world line is a conscious now, and every one exists eternally, side-by-side, as it were, in space-time.  Why do I not experience them all at once.  Why do I only experience THIS one and now THIS one?

I do have my own answer to this question, and it is that we ARE experiencing ALL of our Nows eternally, although somehow only ever in one channel at a time.  Every instance from our first sentient experience through to our last is experienced by us eternally.  Each exists at some event in space-time, but all are there in the eternal 4-D block that is existence.  So we don't get life-after-death as such (because the 'after' shows that we are talking within the time dimension with that phrase), but we do get eternal life!  And that eternal life is no better or worse than each instant that you live.  Moments of suffering are eternal, as are moments of elation, despair and euphoria.  Drink deep.  Live it up!